On Fri, Feb 22, 2019 at 11:04:05AM +0800, Jason Wang wrote: > > On 2019/2/22 上午9:35, Michael S. Tsirkin wrote: > > On Thu, Feb 21, 2019 at 05:40:22PM +0800, Jason Wang wrote: > > > On 2019/2/21 下午4:18, Yuri Benditovich wrote: > > > > > > For 1.0 device, we can fix the queue_enable, but for 0.9x device > > > how do > > > you enable one specific queue in this case? (setting status?) > > > > > > > > > Do I understand correctly that for 0.9 device in some cases the > > > device will > > > receive feature _MQ set, but will not receive > > > VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET? > > > Or the problem is different? > > > > > > > > > Let me clarify, VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET is used to control the the > > > number of queue pairs used by device for doing transmission and > > > reception. It > > > was not used to enable or disable a virtqueue. > > > > > > For 1.0 device, we should use queue_enable in pci cfg to enable and > > > disable > > > queue: > > > > > > > > > We could do: > > > > > > 1) allocate memory and set queue_enable for vq0 > > > > > > 2) allocate memory and set queue_enable for vq1 > > > > > > 3) Set vq paris to 1 > > > > > > 4) allocate memory and set queue_enable for vq2 > > > > > > 5) allocate memory and set queue_enable for vq3 > > > > > > 6) set vq pairs to 2 > > > > I do not think spec allows this. > > > > > > The driver MUST follow this sequence to initialize a device: > > 1. Reset the device. > > 2. Set the ACKNOWLEDGE status bit: the guest OS has noticed the device. > > 3. Set the DRIVER status bit: the guest OS knows how to drive the device. > > 4. Read device feature bits, and write the subset of feature bits > > understood by the OS and driver to the > > device. During this step the driver MAY read (but MUST NOT write) the > > device-specific configuration > > fields to check that it can support the device before accepting it. > > 5. Set the FEATURES_OK status bit. The driver MUST NOT accept new feature > > bits after this step. > > 6. Re-read device status to ensure the FEATURES_OK bit is still set: > > otherwise, the device does not > > support our subset of features and the device is unusable. > > 7. Perform device-specific setup, including discovery of virtqueues for the > > device, optional per-bus setup, > > reading and possibly writing the device’s virtio configuration space, and > > population of virtqueues. > > 8. Set the DRIVER_OK status bit. At this point the device is “live”. > > > > > > Thus vqs are setup at step 7. > > > > # of vq pairs are set up through a command which is a special > > buffer, and spec says: > > > > The driver MUST NOT send any buffer available notifications to the device > > before setting DRIVER_OK. > > > So you meant write to queue_enable is forbidden after DRIVER_OK (though it's > not very clear to me from the spec). And if a driver want to enable new > queues, it must reset the device?
That's my reading. What do you think? > > > > > > > > But this requires a proper implementation for queue_enable for vhost > > > which is > > > missed in qemu and probably what you really want to do. > > > > > > but for 0.9x device, there's no such way to do this. That's the issue. > > 0.9x there's no queue enable, assumption is PA!=0 means VQ has > > been enabled. > > > > > > > So > > > driver must allocate all queBes before starting the device, otherwise > > > there's > > > no way to enable it afterwards. > > > > As per spec queues must be allocated before DRIVER_OK. > > > > That is universal. > > > If I understand correctly, this is not what is done by current windows > drivers. > > Thanks > > > > > > > There're tricks to make it work like what is > > > done in your patch, but it depends on a specific implementation like qemu > > > which > > > is sub-optimal. > > > > > > > > > > > > > > > A fundamental question is what prevents you from just > > > initialization all > > > queues during driver start? It looks to me this save lots of > > > efforts > > > than allocating queue dynamically. > > > > > > > > > This is not so trivial in Windows driver, as it does not have > > > objects for queues > > > that it does not use. Linux driver first of all allocates all the > > > queues and then > > > adds Rx/Tx to those it will use. Windows driver first decides how > > > many queues > > > it will use then allocates objects for them and initializes them > > > from zero to > > > fully functional state. > > > > > > > > > Well, you just need to allocate some memory for the virtqueue, there's no > > > need > > > to make it visible to the rest until it was enabled. > > > > > > Thanks > > > > > > > > > > > >
